A wind turbine known in the art comprises a tapered wind turbine tower and a wind turbine nacelle positioned on top of the tower. A wind turbine rotor with three wind turbine blades is connected to the nacelle through a low speed shaft, which extends out of the nacelle front as illustrated on FIG. 1.
Wind turbine towers typically comprise a number of tapered round tower sections mounted on top of each other. The tower sections are usually bolted together through internally placed horizontal flanges, which are welded to the top and bottom of each tower section. Each tower sections comprise a number of tower rings welded to each other. These tower rings are usually made of steel plates, which are rolled into a circular shape and welded to make them constitute a closed 360° ring.
The general idea behind this design is that, the tower has to be relatively easy to assemble at the mounting site and that a round tower without any visible joints is more pleasing to the eye. But in resent years the development of mass-produced wind turbines has moved towards making them bigger and bigger, both in output and in size. This process calls for better and more cost-efficient components and manufacturing methods, and particularly in the field of wind turbine towers, this development has been profound. The manufacturing facilities for large modern wind turbine towers demands a building with a free height of 8 m, access to lifting equipment with a capacity of 70 t and highly specialised and expensive rolling equipment. Furthermore, welding reduces the towers fatigue limit and thereby its strength, which makes it necessary to make the tower or at least parts of the tower of plates thicker than what otherwise, would be necessary.
European patent application EP 1 561 883 disclose a wind turbine tower made of staggered prefabricated metal parts. The metal parts are formed as long substantially rectangular plates, which are open at the side facing the inside of the tower. The parts are bolted together inside the tower through their adjacent sides. Large annular stiffening ring can be provided to the inside of the tower to improve the towers rigidity. This design provides for a polygonal tower where welding in and between the tower sections are severely reduced or eliminated. But the metal parts have a complex design and are thereby difficult and expensive to manufacture.
An object of the invention is to provide for a wind turbine tower without the mentioned disadvantages.
Especially it is an object of the invention to provide for a cost efficient tower design which provides for a simple tower manufacturing process.
Furthermore, it is an object of the invention to provide efficient means for aiding the assembly of the tower and the succeeding maintenance.